Chemistry 1A, Spring 2007
Midterm Exam 3
April 9, 2007
(90 min, closed book)
Name:__________KEY____________
SID:____________________________
TA Name:_______________________
1.)
Write your name on every page of this exam.
2.)
This exam has 34 multiple choice questions. Fill in the Scantron form AND circle
your answer on the exam.
3.)
There is no penalty for guessing, so answer every question.
4.)
Some questions may require bubbling in more than one choice to receive credit.
Page 1
Name_________________________
E = hν
λν = c
λ deBroglie = h / p = h / mv
Ekin (e-) = hν - Φ = hν - hν 0
Z2
E n = − 2 R∞
n
∆x ∆p ~ h
p = mv
Particle in a box (1-D Quantum):
En = h2n2/8mL2 ; n = 1, 2, 3...
Color and Wavelength of Light
Wavelength (nm)
400
600
800
IR
Red
Green Blue
200
UV
ΔG° = ΔH° - TΔS°
ΔH° = Σ ΔH°f (products) - Σ ΔH°f (reactants)
PV = nRT
3
E kin = RT
2
3RT
v rms =
M
ΔE = q + w
w = - PextΔV
3
ΔE = nRΔT
2
ΔS° = Σ S° (products) - Σ S° (reactants)
N0 = 6.02214 x 1023 mol-1
pX = - log X
R∞ = 2.179874 x 10-18 J
R∞ = 3.28984 x 1015 Hz
ΔG° = Σ ΔG°f (products) - Σ ΔG°f (reactants)
S = kBlnW
ΔG° = - RTln K
ΔH ° 1 ΔS °
ln K = −
+
R T
R
ΔG° = - nFΔЄº
pH = pK a + log
[ A− ]
[ HA]
k = 1.38066 x 10-23 J K-1
h = 6.62608 x 10-34 J s
me = 9.101939 x 10-31 kg
c = 2.99792 x 108 m s-1
Gas Constant:
R = 8.31451 J K-1 mol-1
R = 8.20578 x 10-2 L atm K-1 mol-1
T (K) = T (C) + 273.15
F = 96,485 C / mol
1 V = 1 J / C 1 nm = 10-9 m
1 kJ = 1000 J
Cp(water) = 4.184 kJ/oC·g
Page 2
Name_________________________
1.)
A mixture of 1.00 g of H2 and 1.00 g of He exerts a pressure of 0.480 atm. What
is the partial pressure of each gas in the mixture?
A)
B)
C)
D)
E)
2.)
PH2 = 0.240 atm
PH2 = 0.320 atm
PH2 = 0.160 atm
PH2 = 0.384 atm
PH2 = 0.096 atm
PHe= 0.240 atm
PHe= 0.160 atm
PHe= 0.320 atm
PHe= 0.096 atm
PHe= 0.384 atm
Consider the balanced reaction for the combustion of octanol:
C8H18O (g) + 12 O2 (g) → 8 CO2 (g) + 9 H2O (g)
What volume of carbon dioxide gas will be produced from 5.00 g of octanol and a
stoichiometric amount of oxygen if the reaction is carried out at 28oC and 0.984
atm?
A) 0.308 L
3.)
B) 6.89 L
C) 7.72 L
D) 8.69 L
E) 0.966 L
Which change(s) in a sample of ideal gas would have the same effect on the
pressure as increasing the velocity of the particles? Mark all that apply.
A) Increase in temperature.
B) Increase in volume.
C) Decrease in pressure
D) Increase in the number of moles of gas.
E) None of these.
4.)
What is the pressure required to compress a 1.00 L sample of air at 1.00 atm to
0.400 L at 25°C?
A) 1.0 atm
B) 1.5 atm
C) 2.0 atm
D) 2.5 atm
E) 3.0 atm
Page 3
Name_________________________
For the next three questions, consider four flasks filled with 1.0 mol of different gasses:
Flask A:
Flask B:
Flask C:
Flask D:
O2 at 760 torr and 10oC.
N2 at 900 torr and 80oC.
He at 800 torr and 10oC.
He at 500 torr and 80oC.
5.)
Which flask(s) will have molecules with the greatest average kinetic energy? B, D
6.)
Which flask(s) will have molecules with the greatest root mean square velocity? D
7.)
Which flask(s) will have the greatest number of collisions per second with the
walls of the container? B
For the next four questions consider a system which releases 546 kJ of heat while its
internal energy drops by 125 kJ.
8.)
What can you infer about the process? Mark all that apply.
A) Work is involved.
B) The entropy of the system decreases.
C) It is spontaneous.
D) The first law of thermodynamics does not apply.
9.)
Based on the information given, which relationship(s) should be used to calculate
the amount of work involved? Mark all that apply.
A)
B)
C)
D)
E)
10.)
w = -P ∆V
∆E = q + w
qsystem = qsurroundings
w = -RTlnK
S = kBlnW
How much work is done (if any) in kJ?
A) -125
11.)
B) -421
C) +125
D) +421
E) 0
What best characterizes the work done?
A)
B)
C)
D)
Work is done on the system.
Work is done by the system.
Work is done both on and by the system.
Cannot determine based on the information provided.
Page 4
Name_________________________
12.)
A system undergoes a change that can be broken down into two steps: 1) the
system does 70 J of work while absorbing 62 J of heat, and 2) the system releases
29 J of heat while 94 J of work is being done on it. What is the overall energy
change of the system?
A) +57 J
13.)
B) -57 J
C) +9 J
D) -9 J
E) +255 J
Consider the chemical reaction that occurs in a hydrogen fuel cell:
2 H2 (g) + O2 (g) → 2 H2O (l)
ΔH = -572 kJ
What is the heat change (in kJ) when 186 g of oxygen reacts with excess
hydrogen?
A) -572 0
14.)
C) +3320
D) -3320
E) -1660
Consider the following reactions carried out at a constant temperature and
pressure. In which of these will the amount of work done be positive? Hint: only
the coefficients of the reactants are given. All species are gas unless otherwise
noted.
A)
B)
C)
D)
E)
15.)
B) +5720
The synthesis reaction of 2 mol SO2 and 1 mol O2 to give SO3.
The synthesis reaction of 4 mol NO to give O2 and N2.
The decomposition reaction of 2 mol CCl2O to give CO and Cl2.
The combustion of 2 mol CH3OH.
The conversion of 2 mol of solid I2 to gaseous I2.
Consider the reaction for which ΔHo~200 kJ/mol and ΔSo~100 J/mol
CaO (s) + CO2 (g) → CaCO3 (g)
Under which condition(s) will this reaction be spontaneous?
A)
B)
C)
D)
At high temperatures.
At low temperatures.
The reaction will always be spontaneous.
The reaction will never be spontaneous.
Page 5
Name_________________________
16.)
A 46.2 g sample of Cu is heated to 95.4oC and then placed in a calorimeter with
75.0 g of water at 19.6oC. The final temperature of the water is 21.8oC. What is
the heat capacity of the Cu in kJ/ oC·g if the calorimeter does not absorb any heat?
A) 0.203
B) -0.203
C) 0.0770
D) -0.0770
E) 4.18
Use the following phase diagram to answer the next three questions:
P
L
C
S
B
D
C
A
G
A
Tc
T
17.)
Along which isotherm(s) will a phase change be observed? Mark all that apply.
A) A
18.)
A)
C) C
D) D
E) none of these
Along which line will there be a positive change in entropy? Mark all that apply.
A) A
19.)
B) B
B) B
C) C
D) D
E) none of these
Which of the following represents a plot of the vapor pressure vs. T?
B)
C)
D)
Page 6
Name_________________________
For the next five questions, consider the gas phase reaction N2 + 3 H2 ↔ 2 NH3 with an
equilibrium constant of K = 0.278 at 800 K. The entropies of formation (in kJ/mol) are:
H2=130.6, N2=191.5, & NH3=192.3.
20.)
What is the standard entropy change associated with this reaction (J/mol)?
A) –198.7
21.)
E) 198.7
B) +84.0
C) -8.51
D) +8.51
E) +4.26
B) 0.248
C) 2.90
D) 1.91
E) 0.881
Which best describes the condition of the reaction mixture in the previous
question?
A)
B)
C)
D)
24.)
D) 129.8
Analysis of a reaction mixture yielded the following partial pressures: N2 = 0.417
atm, H2= 0.524 atm and NH3= 0.122 atm. What is the reaction quotient for the
reaction?
A) 0.116
23.)
C) -99.4
Which is the free energy change associated with this reaction in kJ/ mol?
A) –84.0
22.)
B) –129.8
The reaction mixture is at equilibrium.
The reaction mixture is not at equilibrium – it will proceed toward reactants.
The reaction mixture is not at equilibrium – it will proceed toward products.
Can’t tell.
If equilibrium is reached for this reaction, and the volume of the container is then
reduced by a factor of two. Which best describes how the reaction mixture will
proceed?
A) Toward products.
B) Toward reactants.
C) No change.
Page 7
Name_________________________
Consider the following three reactions for the next two questions:
25.)
N2 (g) + 2 O2 (g) → 2 NO2 (g)
K2
3)
2 NO (g) + O2 (g) → 2 NO2 (g)
K3
B) (K1)2 K2
C) K1 K2
D) K1/K2
E) 1/(K1)2
What is the effect on reaction 3 if the partial pressure of NO is increased at
equilibrium?
an decrease in the partial pressure of O2
a shift toward reactants
a shift toward products
a change in the K1
none of these
Given that the reaction is endothermic, what is the effect of increasing the
temperature of reaction 1 at equilibrium? Mark all that apply.
A)
B)
C)
D)
E)
29.)
2)
What is an expression for K3?
A)
B)
C)
D)
E)
28.)
K1
PN2 PO2 / PNO
PNO / PN2 PO2
PN2 (PO2)2 / PNO
PNO PN2/ (PO2)2
(PNO)2 / PN2 PO2
A) K2/K1
27.)
N2 (g) + O2 (g)→2 NO (g)
What is an expression for the reaction quotient for reaction 1?
A)
B)
C)
D)
E)
26.)
1)
An decrease in the partial pressure of O2.
A shift toward reactants.
A shift toward products.
A change in K1.
None of these.
What is the reaction quotient after the volume is halved for reaction 1 at
equilibrium?
A) Q = K1
B) Q = 2K1
C) Q = ½ K1 D) Q = ¼ K1 E) Q = 4K1
Page 8
Name_________________________
30.)
Which of the following is the correct plot of ΔGo vs. T for the evaporation of
water?
A)
31.)
B)
C)
D)
The equilibrium position is quantified by the equilibrium constant, K. Which of
the following generalized statements regarding K is false? Mark all that apply.
A) When K is larger than 1, the equilibrium position favors the formation of
products.
B) When K is larger than 1, the value of ΔGo for the reaction is always negative.
C) When K is equal to 1, the number of moles of reactants is always equal to the
number of moles of product.
D) When K is larger than 1, the forward reaction is always occurring faster than
the reverse reaction is.
E) When K is smaller than 1, the value of ΔH for the reaction is always negative.
32.)
In order to determine the identity of a compound with a molecular formula of CxHy
you carry out an experiment with a Dumas bulb. In a bath of boiling water, you
determine that a 2.0 L Dumas bulb will hold exactly 1.829 g of gaseous unknown.
If the atmospheric pressure is 1.0 atm, what is the identity of your unknown?
A) CH4
33.)
B) C2H2
C) C2H4
D) C2H6
E) C3H6
Recall the experiment that you did in lab to determine ΔH for the reaction between
magnesium oxide and hydrochloric acid. Which of the following would result in
ΔH value that is more exothermic than the actual value?
A) The top of the calorimeter is not on tightly.
B) The student accidentally put some ice into the calorimeter when determining
the calorimeter constant, Kcal.
C) The heat capacity of the solution is actually smaller than the heat capacity of
pure water.
D) None of the above will result in a low enthalpy of reaction.
Page 9
Name_________________________
34.)
Potassium thiocynate (KSCN) is a very soluble salt. Iron thiocyanate is a red
complex ion that forms from the combination of iron (III) which is yellow and
thiocynate ions which are transparent:
Fe3+ + SCN- ↔ FeSCN2+
The equilibrium constant for the formation of iron thiocynate is moderate. What
will happen to the color of the solution as potassium thiocynate is introduced into a
test tube containing equal amounts of iron and thiocyanate?
A)
B)
C)
D)
E)
The color will not change.
The solution will become redder.
The solution will become more transparent.
The solution will become more yellow.
Cannot determine the color change based on the information provided.
Page 10